Do you mean in the general page menu? If you right click on a tab itself you should get the close option.
you simply don't know what the context menu is.
right click anywhere on a page to bring out the context menu
Right-click on a tab to see the contextual menu with Close Tab.
You can use the Menu Editor extension to move menu items around.
thankyou for your message
i know there are plenty of addons that can handle the job
i am in fact looking for whether there is a user setting capable of this
i found two other addons that can do the same thing.
will check out the one you said in your message
'cause the context menu of my firefox is getting longer and longer !
Yep, the length of contextual menus is why I use the Menu Editor extension.